The Embryonic Stem Cell Core (ESC Core) is responsible for: . creating and providing state-of-the-art reagents for the production of targeted mutations in embryonic stem cells. . creating and maintaining quality controlled embryonic stem cell lines from a variety of mouse backgrounds. . teaching the methodology of embryonic stem cell culture and manipulation. The ESC Core also provides consultative services for Siteman Cancer Center (SCC) members when they are designing knock-out or knock-in vectors, and it creates and distributes user-friendly plasmids that facilitate the generation of targeting vectors. The ESC Core also attempts to assist all users with blastocyst injections if injection facilities are not available to that laboratory. By providing a comprehensive service, the ESC Core facilitates the production of gain-of-function and loss-of-function mouse models for SCC faculty.